IL-17 promotes a proinflammatory cytokine milieu in the joint, stimulating the production of IL-1 and tumor necrosis factor α (TNFα) from macrophages (18), and synergizes with these to increase IL-6 and IL-8 production from RA synoviocytes (19,20), the latter being important in neutrophil recruitment. Here, IL17A is linked to rheumatoid arthritis.